Managing the catastrophic risk of underground transformer fires

Abstract

Increasing levels of underground mining mechanisation require the transmission and use of greater quantities of energy. This heightens the risk of underground mine fires occurring in confined spaces, e.g. in transformer bays, on diesel or electric mobile equipment, or in battery charging bays. This paper describes a comparative assessment tool that was developed for the management of fire risks posed by electrical distribution transformers in underground mining operations. When a transformer experiences power surges due to transformer malfunctions, network overloading, or short-circuiting, the ‘fault’ energy is released uncontrollably. In worst-case scenarios, the dielectric oil used to cool transformers may be ignited resulting in a significant conflagration dispersing smoke and toxic gases into the mine’s ventilation network. The violent reaction could trigger a fire that may result in catastrophic consequences for the mining operation. This risk must be well understood and actively managed. The fire risk assessment tool described in this paper has been developed for this purpose. It has been used to assess objectively the impact of various protective and mitigating interventions aimed at reducing transformer fire risks. The tool has been applied to evaluate transformer fire risks across a fleet of over 1,000 distribution transformers in underground applications globally. The tool uses a high-level screening methodology to provide a semi-quantitative systematic approach to rank the assessed risk values and to assist the selection of appropriate single, or groups of, mitigating and/or preventative measures. The tool was developed in consultation with underground mining and utility industry experts, relying on industry data, international standards, guidelines, and expert panel judgement. The tool brings rigour and a standardised approach to assess transformer and associated protection measures to yield objective and globally comparable risk rankings across diverse installations.